JPS5884523A - Oscillating circuit - Google Patents

Abstract

PURPOSE:To obtain an output of an oscillating frequency corresponding to the fluctuation of power supply voltage, by feeding back an inverter circuit output at the odd number of stage of the oscillating circuit which is subjected to capacitor modulation to the ring oscillator consisting of the inverter. CONSTITUTION:Inverters NOT1, NOT2, NOT3 are cascade-connected to form a ring oscillator. Modulation is applied to the oscillator from a capacitor C. A transistor TR1 which is controlled with a power supply voltage VE is provided in a feedback path from the output of the inverter NOT3 to the input of NOT1. Thus, the capacitor C and the resistance value of the TR1 form a CR feedback circuit to obtain the output of oscillating frequency in response to the fluctuation of the power supply voltage VE.

Description

[Detailed Description of the Invention] This invention relates to an oscillation circuit used for driving a thermoelectric printer, for example. Conventionally, the printing mechanism of an office machine with a printing function or a calculator with a printer has been a hammer type, a thermoelectric printer, etc. Type (thermal), Inkzoe, Toni, etc. are mainly used. ・The thermoelectric printer mentioned above brings a metal head with a built-in filament into contact with heat-sensitive glint paper, and passes an electric current through the filament. It prints by changing the color of the paper by generating heat, and is configured as shown in 1 rattan 1rIAK, for example. That is, a capacitor C is connected to both ends of the power supply Vm, and a series circuit of a CIB and a regulator circuit 110 is provided, and the potential at both ends of the capacitor CD is supplied to the control circuit 12. Then, the control circuit IIK and the thermal conductor 11.・
. . 13 is selected in response to the print command, and the selected thermal head 13. ... 13 to print on the print paper 74.

The operation of the control circuit 11 is controlled by the output of the oscillation circuit shown in FIG. This oscillation circuit is a 90-liter oscillator circuit in which capacitor modulation is applied to a ring oscillator using a three-stage inverter circuit.In other words, the cascade-connected inverter circuits N0TI, NOT, OFF.

The power supply VDD is supplied to the inverter circuit NOT, O through the diode D1, and the inverter circuit NOT, O output is fed back to the connection point aK through the capacitor C, and the output of the inverter circuit NOT is fed back through the resistor R. The connection point a on the signal end side of N0-1 is grounded via diode D, and each of the above inverter circuits NOT 1 to NO
T @ JIC supplies power VID to oscillate.

The waveforms at each connection point a-d in the O circuit in Figure 2 above are shown in the third diagram.
As shown in the figure.

Such a thermoelectric! In the case of a rinsing type device, the density of characters or symbols printed on printing paper is proportional to the thermal energy applied to the paper.This thermal energy is the integral value of nine currents flowing into the filament of the thermal head. If the thermal energy applied to the paper and the filament is not constant, the density of the printed letters and symbols will be uneven. Therefore, in the case of thermoelectric printing, it is necessary to keep the thermal energy applied to the paper constant.

However, in recent years, calculators with links and office machines with blinkers have been improved to make their parts lighter, and as a result, power supplies have been forced to be smaller. The current capacity decreases, and the output potential and output current of the power supply decrease during printing that requires a large amount of energy, that is, a large current. Therefore, as described above, the thermal energy applied to the print head changes, resulting in uneven density of characters and symbols.

To solve this problem, normally, as shown in Figure 1, a smoothing TCM is installed externally between both ends of the power supply (V) that applies the filament (K) to the printer. Measures are taken to ensure that the voltage V= applied during driving does not drop, and that a constant current 1 is always supplied to the filament (K).

However, even if the above measures are taken, the amount of current used to generate thermal energy is actually very large, resulting in a slight voltage drop, which causes the amount of current to fluctuate, resulting in some uneven printing. The current situation is also that capacitor C1
In general, a capacitance of about 1000 fiF is required, and capacitors with a capacitance value of this class are of normal capacity (generally speaking, most external capacitors for 1tcLsr are 1μF or less). It is very large in size and expensive compared to K.For this reason, providing a smoothing capacitor is a major hindrance to making printers smaller and lighter and lowering the cost of equipment. In addition, this method has the disadvantage that the print density becomes thinner as the output voltage decreases due to the life of the power supply.This invention was made in view of the above circumstances.
The purpose of this is to change the time of the print command signal from the control circuit so that the print head always supplies constant thermal energy to the print paper in response to the current supplied to the print head. It is an object of the present invention to provide an oscillation circuit that can change the oscillation frequency in response to voltage fluctuations, and can reduce costs by reducing the number of external components.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. Figure 4 shows its structure, and the same components as in Figure 12 are given the same reference numerals and their explanation will be omitted. That is, a transistor Trl whose conduction is controlled by a power supply voltage V is provided along the path of the inverter circuit NoT*tvR.

According to such a configuration, in the case of the circuit shown in FIG. 2, the number of oscillations 1Ill#jL is determined by K C1l as expressed by /-K. , in the case of the circuit shown in No. 411, the resistance value depends on the value of the voltage v applied to the F transistor Trl (r-), so if this resistance value is Rt (Vm), the oscillation local liquid number is becomes. Therefore, the oscillation frequency of this circuit depends on the value of the power supply voltage V, O')tC, the power supply for glint is applied to the transistor f-), and the ζO transistor is connected to the CR oscillation circuit. By using it as a feedback resistor, fluctuations in the power supply voltage are detected and the oscillation frequency of the oscillation circuit is changed.

The operation of the above-mentioned configuration will be explained using the tie chart shown in FIG. First, inverter circuit NO? ,
When the output potential of Vya is reversed from positive to negative, the potential difference between both ends of capacitor C remains unchanged, and the potential of connection point a instantaneously becomes rVoo + Vy J. This is the voltage stored in Vya capacitor CI. -At this time, the output potential of the inverter circuit NOT is at the Vll level. Next, since a bias of potential vl is applied to the transistor Tr@0j)a) and it is in an on state, the charge accumulated at the connection point aK is discharged to the connection point dK via the transistor Trl. The waveform of the potential change at the connection point d at this time is represented by the differential waveform of a differential circuit based on the on-resistance of the capacitor C and the transistor Tr1 and K, and its time constant is CBy
(v++) T is present, and the connection point mO potential is in/
4-Event circuit NOT l threshold voltage V? 11C
When it happened, W! When the voltage at the connection point is equal to the potential v1, the connection point is reversed from negative to positive.In this state, the potential at the connection point fi is
rV, , -Vν. As in the case described above, the nine electric currents stored at one connection point a are discharged to the connection point d via the transistor Tr1, and the potential at the connection point @O has a differential waveform.

In this way, the potential at the connection point a becomes V! When the voltage reaches C, the potential at the connection point bo becomes VBD, and the potential at the connection point e becomes Vll, and the above-mentioned cycle is sequentially repeated.

At time t, when printing starts, the power supply potential Vl shows a voltage dog due to energy consumption, as shown in FIG. 5. Then, the transistor Tr @
The applied bias voltage decreases, and the on-resistance of the transistor Trl increases. Therefore, the time constant CRt (Vm) of the differential circuit described above increases, and the differential waveform becomes elongated as shown in the figure. As a result, as the oscillation period increases by 2 steps in the power supply potential VmO, the oscillation frequency gradually decreases.The oscillation wave number at this time is equal to the increase in the resistance value of the transistor Tr1.
proportional to quantity. Therefore, a constant amount of thermal energy can always be supplied to the thermal head even without the smoothing capacitor CI. Figure 6 shows another embodiment of the present invention, in which the feedback transistor in the circuit of Figure 4 is shown. A transistor Try (N channel) of opposite polarity is provided in parallel with 〒rl (P channel), and the inverter circuit NO, ,
NOT, , NOT, uses a V cap as the power supply. Therefore, the above transistor Tr snow? -) is grounded, and the power supply voltage V is applied to the pack F. According to such a configuration, it is possible to correct the distortion of the oscillation liquid form of the circuit shown in FIG. Figure 4 O
In the circuit, a transistor Trl acts as a variable resistor.
The on-resistance of is when the connection point & is negative and the connection point d is positive,
It is different when the connection point 1 is positive and the connection point d is negative, and the resistance value becomes larger in the latter case. This causes a pack dart effect when the potential at the connection point a changes from positive to negative. It is from. For this reason, a difference in time constant occurs between the former and latter cases, resulting in distortion of the de-tee within the same cycle. Also, a pack? -) If the shift amount of the threshold voltage due to the effect becomes too large compared to the potential V, and the potential at the connection point a reaches VtwcK, oscillation may stop. In order to cancel the pack r-) effect, a transistor Try of the opposite polarity to the transistor t1 is connected in parallel, so that the oscillation duty is brought closer to the opportunity, and at the same time, the oscillation is prevented from stopping. There is. Here, the inverter circuit N0TI,
NOT, .

The power supply of NOT is set to Vm because tisVoo (if it remains D, rVBo > VmJ, and a forward current of the diode occurs due to the structure of the transistor Try.) At ζζ, the substrate potential of the transistor Trl is set to vDD.
If it is set to K, no forward current will occur, but in this case, the transistor Trl has an r-tobias of 1k, which is unrelated to Vm.
J > Operates as a constant resistance and exhibits oscillation characteristics different from the circuit described above. Figure 7 shows another embodiment of the present invention. In this circuit, the inverter circuit N
Along the feedback path of 0Ts, the transistor Tr1 and the resistor R
1, and a resistor R1 is provided in parallel with this series circuit, and the conduction of the transistor R1 is controlled by the potential V+s. In such a configuration, the function of the resistor yh1o will be explained first. Now, for the purpose of keeping the thermal energy constant, an ideal oscillation frequency characteristic unique to each thermoelectric printer is required, but the ideal characteristic and the frequency that can be obtained can only be determined by the on-resistance value of the transistor Trl. There are many cases where the characteristics do not match. In such a case, first adjust the frequency characteristics in the low frequency region (state II where Vm is low), and then adjust the transistor Trl so as to obtain a frequency higher than the ideal frequency in the high frequency region (state where v-modulus is low). By connecting the constant resistor R1 in series with the transistor Tr1 to set each constant, the reduction rate of the feedback resistance in the high frequency region is suppressed, and the zero-order resistor R, which obtains a frequency characteristic close to the ideal, is:
This function is the same as that of the transistor Tr for effect correction and oscillation stop prevention in the circuit shown in Figure 2 above, and at the same time it also enables frequency matching in the low frequency range. Here, usually R1) Rt
It is.

FIG. 8 shows the ideal frequency characteristics and the -0 frequency characteristics of the circuit shown in FIG.

However, this invention is not limited to the above embodiments, and can be implemented with various modifications.
Inverter circuit NO in the circuit shown in the figure and FIG. 7? ,
, NOT, , N0Ts power supply VmK may be replaced. In addition, in the circuit of Fig. 7, the resistance 8 is set to 5.
It goes without saying that a transistor with a polarity opposite to that of the transistor Trl may be provided as in the circuit shown in the figure.

As explained above, according to this invention, the r-t is connected to the power source along the #Ill path of the odd-numbered inverter circuit in an oscillation circuit in which a ring oscillator consisting of a plurality of inverter circuits is subjected to capacitance modulation. Since a feedback means including a transistor whose conduction is controlled by a potential is provided, the oscillation frequency can be varied in response to fluctuations in the power supply voltage, and the number of external parts is small, making it possible to reduce costs. Because a vibration circuit is obtained.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of the thermoelectric Grinpo, Figure 2 is the above 11
Figure 114 shows a conventional oscillation circuit that performs 107''9-interval control.
A diagram showing an oscillation circuit according to an embodiment of the invention, FIG. 5 is a tie chart showing potential changes at each connection point O in the circuit shown in FIG. 4, and FIGS. FIG. 8, a circuit diagram showing another embodiment, is a characteristic diagram showing frequency characteristics and ideal frequency characteristics in the circuit of the seventh WA. NOT,~NO? ,--inverter circuit, C...
Capacitor, Trl*Try...transistor,
R1, R■-・Resistance, V-tension...Power supply voltage Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 5 Figure 6

Claims (4)

[Claims] (1) A plurality of cascade-connected inverter circuits and a capacitor that feeds back the output of the even-numbered inverter circuits;
An oscillation circuit comprising feedback means for feeding back the output of an odd-numbered inverter circuit in response to fluctuations in power supply voltage. (2) The above feedback means is composed of a transistor, and its r
-) is conduction-controlled by a power supply voltage. (3) What is the above means of return? -) is a transistor whose conduction is controlled by the power supply voltage? 2. The oscillation circuit according to claim 1, wherein transistors r-) and (r-) of opposite polarity to which a power supply voltage is applied are connected in parallel. (4) The above-mentioned feedback means comprises a series circuit of a transistor and a resistor (r-) whose conduction is controlled by a power supply voltage, and a resistor connected in parallel to this series circuit. The oscillation circuit according to item 1.